Managing Alerts for Site Users

In MOSS site collection, you can manage alerts for site collection users, by adding them to the new alert created, as soon as you add the users, every user will get an email indicating that a new alert has been created for him.

To delete or unsubscribe users' alerts on behalf of them, you can browse to, Site Actions -> Site Settings -> User Alerts
Select the user from Display Alerts For dropdown list, and then click Update, check the alert you want to delete and then click Delete Selected Alerts.

For multi-lingual site collections, if you try to manage users' alerts from the site settings of the site collection ( language label site collection ), you will not get users listed in the dropdown list, this is a special case for multi-lingual site collections, the alerts are not shown for language label site collections, if you want to manage the alerts you will have to jump one more level up, to the Variation Home site settings, and then you will get all the language dependent users' alerts listed.